Conventionally, there has been widely used an active matrix liquid crystal display device which includes a bus line, such as a gate bus line, between adjacent pixels.
In the above active matrix liquid crystal display device having a vertically aligned liquid crystal, an electric field generated by the bus line may cause discontinuity in the alignment direction of liquid crystal molecules which lie in a region of the pixel electrode which region faces the bus line. This deteriorates the display quality. The following description explains this with reference to FIGS. 6, 9, and 10 (a) through 10 (b).
FIG. 9 (a) is a partial plan view of conventional pixel electrodes 102 in adjacent pixels between which no gate bus line 142 is disposed. FIG. 9 (b) is a partial plan view of conventional pixel electrodes 102 in adjacent pixels between which a gate bus line 142 is disposed.
FIG. 6 (a) shows how liquid crystal molecules in the pixels shown in FIG. 9 (a) align. FIGS. 6 (b) and 6 (c) show how liquid crystal molecules in the pixels shown in FIG. 9 (b) align. As shown in FIGS. 9 (a) and 9 (b), the gate bus line 142 between the adjacent pixels is disposed in a direction which crosses a source bus line 143 orthogonally and is parallel to one side of each of the pixel electrodes 102.
In a case of the conventional pixel electrodes 102 in the adjacent pixels between which no gate bus line 142 is disposed, as shown in FIG. 6 (a), the liquid crystal molecules align radially from an alignment controlling projection 115 which is provided on a counter electrode.
Meanwhile, in a case of the conventional pixel electrodes 102 in the adjacent pixels between which a gate bus line 142 is disposed, the alignment of the liquid crystal molecules in each of regions S9 and S10 is different from the alignment in the other region of the corresponding one of the pixel electrodes 102 (see FIGS. 6 (b) and 6 (c)). The regions S9 and S10 are regions of the respective pixel electrodes 102 which regions face the gate bus line 142. This alignment abnormality has two types as shown in FIGS. 6 (b) and 6 (c), respectively. When not only one of these types, but multiple types of alignment state occur, display irregularity is caused, and thereby the display quality is deteriorated. In other words, occurrence of alignment abnormality causes no display irregularity if the alignment state has only a single type.
The following description deals with discontinuity of an alignment direction of liquid crystal molecules 121. This discontinuity causes the above multiple types of alignment state.
FIG. 10 (a) is a cross-sectional view taken along line A-A of FIG. 9 (a), i.e., taken along line G-G of FIG. 6 (a). FIG. 10 (b) is a cross-sectional view taken along line B-B of FIG. 9 (b), i.e., taken along line H-H of FIG. 6 (b).
In a case of the conventional pixel electrodes 102 in the adjacent pixels between which no gate bus line 142 is disposed, no discontinuity is caused to the alignment direction of liquid crystal molecules 121 between the adjacent pixel electrodes 102 (see FIG. 10 (a)).
In contrast, in a case of the conventional pixel electrodes 102 in the adjacent pixels between which a gate bus line 142 is disposed, discontinuity is caused to the alignment direction of liquid crystal molecules 121 between the adjacent pixel electrodes 102, i.e., above the gate bus line 142 (see FIG. 10 (b)).
This is apparently because the equipotential line is distorted by the influence of the gate bus line 142, and the distortion causes discontinuity in the alignment direction of the liquid crystal molecules 121. This distortion of equipotentiality is likely to occur particularly when the gate bus line 142 has a deep negative polarity.
This discontinuity of the alignment direction occurs in plural types and in an irregular manner. This causes deterioration in the display quality.
In view of this, the following arts are suggested for the purpose of reducing such deterioration in display quality.
Patent Document 1 suggests an art for additionally providing a light-blocking member which covers a bus line. The light-blocking member is provided so as to prevent light leakage caused by discontinuity of the alignment direction of liquid crystal molecules in a region adjacent to the bus line.
For the same purpose as described in Patent Document 1, Patent Document 2 suggests an art for providing pixel electrodes that partially overlap a bus line. It is intended by this art that, by overlapping the bus line with the pixel electrodes, it becomes impossible for an oblique electric field generated at the edges of the bus line to influence liquid crystal molecules, thereby to consequently reducing discontinuity of the alignment direction of the liquid crystal molecules.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 313197/1993 (Tokukaihei 5-313197; published on Nov. 26, 1993)    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 70151/2005 (Tokukai 2005-70151; published on. Mar. 17, 2005)